The invention is based on a hydraulic brake system with an anti-skid system and traction control for a vehicle, as defined hereinafter.
A vehicle brake system of this type has already been proposed in which a precharging pump and a return pump are driven independently of one another. When the traction control is operative, the precharging pump, embodied as a low-pressure pump with a high pumping flow pumps brake fluid to the inlet of the return pump. The return pump, which is capable of pumping brake fluid at high pressure and a low pumping flow compared with the precharging pump, forces brake fluid into the wheel brake cylinder of the spinning vehicle wheel upon pressure buildup. However, while the traction control is operative, a pressure buildup is required for only a relatively short length of time. For the period of time including the phases of pressure holding and pressure reduction during traction control, the brake fluid pumped by the return pump must therefore be diverted, for instance via a pressure limiting valve, which can mean that the brake fluid is heated considerably. To reduce this power loss, it has been proposed that the drive motor of the precharging pump be triggered in pulsed fashion subsequent to the initial filling of the wheel brake cylinder during traction control, in order in this way to reduce the pumping flow of the return pump. Because of the high turn-on current intensity of the drive motor, this triggering is attainable only at great expense.